How can i clone only one part after it was touched?

you can add a variable that makes the function run once like this :

local already_cloned = false -- we will use this variable to make the script excute once only.

script.Parent.Touched:Connect(function(hit)
if hit.Parent:FindFirstChild("Humanoid").Health then
	 if already_cloned == false then -- if we havent cloned before then
hit.Parent:FindFirstChild("Humanoid").Health = hit.Parent:FindFirstChild("Humanoid").Health - 100
local part = workspace.Part
script.Parent:Destroy()
local copy = part:Clone()
copy.Parent = part.Parent
copy.Position = Vector3.new(10,20,10)
  already_cloned = true --after we clone once then "already_cloned" should be set to true since we already cloned it and dont want to clone again.
 end
    end
end)